The invention relates to a drivetrain comprising a friction clutch disposed within the frictional connection between an internal combustion engine and a transmission and having an input part connected to the internal combustion engine and at least one output part connected to a transmission input shaft, as well as a disengagement device for the latter.
In a known way, friction clutches are operated via a hydraulic disengagement system comprising a manually or automatically operated master cylinder and a slave cylinder that disengages the clutch, both cylinders being connected by a hydraulic line. In so-called forced-compression clutches, the clutch is disengaged in the force-free state of the clutch, and the frictional engagement for connecting internal combustion engine and transmission is accomplished by actuation and holding of the slave cylinder under pressure via the master cylinder. In particular for dual clutches in which a common input part is branched into two output parts, each having a transmission output shaft, the connection of the clutches in this manner is advantageous. If both or one of the two disengagement devices fails, for example by loss of pressure medium, these clutches are always open and do not lock the transmission, as is the case for clutches, for example, that are normally engaged in the force-free state.
Friction clutches of the type mentioned above are usually used, in addition to manually operated transmissions, in automated transmissions, for example in automated shift transmissions (AST) or dual clutch transmissions (DCT), which are generally driven by a control device, both the clutch and the engagement and disengagement of the gears being operated automatically. If a control device of this type fails, it may happen, depending on the control strategy used, that the clutch position of one clutch or, in a dual clutch transmission, of both clutches is/are frozen, and therefore the operation of the internal combustion engine can no longer be controlled, regardless of the transmission output speed, and thus the wheel speed is no longer controllable; that is, when the vehicle is at a standstill, for example, operation of the internal combustion engine to provide power to accessory units is no longer possible.